1. Field of the Invention
The present invention relates to a cleaning unit for removing residual toner on a photoreceptor drum surface for use in an image forming apparatus such as an electrophotographic copying machine and printer, and more particularly, to a cleaning unit for removing residual toner by user of a fur brush.
2. Description of the Prior Art
Conventionally, a cleaning unit for removing residual toner on a surface of a photoreceptor drum is provided. The cleaning unit is arranged at a portion corresponding to a downstream side of a transferring process so as to face the surface of the photoreceptor drum. As shown in FIG. 1, a fur brush 4 whose tip is in contact with the surface 1 is arranged in the cleaning unit. To the fur brush 4, a recovering roller 5 is provided so that the tip of the fur brush is in contact therewith. In the downstream side of the fur brush 4, a blade 301 whose one end is in contact with the surface 1 is arranged in order to remove toner which cannot be removed by the fur brush 4. Moreover, at a position below the recovering roller 5, a toner tray 303 for storing removed toner and a screw roller 304 for returning the toner gathered in the toner tray 303 to a toner hopper are arranged. One end of the toner tray 303 is arranged to adjoin the surface 1 so that the removed toner does not spill out of the tray 303. Below the recovering roller 5, a blade 302 for removing toner adhering to the roller 5 is arranged so as to be in contact therewith. To the fur brush 4 and the recovering roller 5, potential applying means 6 is connected for separating residual toner from the surface 1 by electrically attracting it.
A part of toner which has not been transferred remains on the surface 1 where toner has been transferred onto a copy sheet by the transferring process 2. The surface 1 to which the residual toner adheres rotates to the fur brush 4. Since the fur brush 4 rotates and is provided with a potential of a pole reverse to that of the toner by the potential applying means 6, the residual toner adheres to the brush 4 because of frictional force and electrical attraction. The toner adhering to the fur brush 4 is conveyed to the recovering roller 5. When the brush is in contact with the surface of the roller, the toner adhering to the fur brush 4 is attracted by the recovering roller 5 and adheres thereto, since the recovering roller 5 is provided with a potential higher than that of the fur brush 4. The toner adhering to the recovering roller 5 is rubbed off by the blade 302 which is in contact with the roller 5, and is dropped onto the toner tray 303.
Moreover, since the residual toner cannot completely be removed only by the fur brush 4 because of electrical attraction between the toner and the surface 1, a part of the toner still remains on the surface 1. Although the remaining toner is mechanically removed by the blade 301, a part of toner adheres to the edge of the blade 301.
In order to separate residual toner from the surface 1, it is necessary that the number of rotation of the fur brush 4 be approximately 200 rpm. Because of the rotation of the fur brush 4, the residual toner scatters. The blade 301 arranged in the downstream side of the fur brush 4 also prevents the scattering of toner.
As described above, however, the toner adhering to the edge of the blade 301 re-adheres to the surface 1, whereby mal-cleaning occurs in a copying operation for a first copy sheet. Moreover, the adhesive power of granular and spherical toner to the surface 1 is so strong that cleaning cannot effectively be performed by a conventional cleaning unit which employs a fur brush or a blade.
Moreover, in this prior art, to the fur brush 4 which is in contact with the surface 1, a positive voltage E1 is applied by a DC current source 6. Because of this, the fur brush 4 electrostatically attracts negatively charged toner remaining on the surface 1. However, since the positively charged toner cannot be recovered from the surface 1, it is impossible to recover the positively charged toner onto the recovering roller 5. Therefore, in this prior art, residual toner adhering to the surface of the photoreceptor drum cannot completely be removed.